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Tune Lossless compression for lower qualities.

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This is required for WebP lossy+Alpha images, where Alpha channel is taking
60-70% of the compression (CPU) cycles.

Also evaluated on 1000 PNG corpus and overall compression speed
is 15-40% better for lossy (PNG+Alpha) compression.
The pure lossless compression numbers are almost same (or little
better) with this change.

Change-Id: I9e5ae7372ed6227a9a5b64cd9cff84c747195a57
This commit is contained in:
Vikas Arora 2013-03-05 22:05:00 +00:00 committed by James Zern
parent 19eb012c55
commit 0478b5d214
3 changed files with 6 additions and 11 deletions
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2
src/enc/alpha.c
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@ -80,7 +80,7 @@ static int EncodeLossless(const uint8_t* const data, int width, int height,
config.lossless = 1;
config.method = effort_level; // impact is very small
// Set a moderate default quality setting for alpha.
config.quality = 6.f * effort_level;
config.quality = 5.f * effort_level;
assert(config.quality >= 0 && config.quality <= 100.f);
ok = VP8LBitWriterInit(&tmp_bw, (width * height) >> 3);

8
src/enc/backward_references.c
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@ -555,10 +555,10 @@ static int BackwardReferencesHashChainDistanceOnly(
}
// 2) Add to the hash_chain (but cannot add the last pixel)
{
const int last = (len < pix_count - 1 - i) ? len
: pix_count - 1 - i;
for (k = 0; k < last; ++k) {
HashChainInsert(hash_chain, &argb[i + k], i + k);
const int last = (len + i < pix_count - 1) ? len + i
: pix_count - 1;
for (k = i; k < last; ++k) {
HashChainInsert(hash_chain, &argb[k], k);
}
}
// 3) jump.

7
src/enc/histogram.c
View File

@ -390,17 +390,12 @@ int VP8LGetHistoImageSymbols(int xsize, int ysize,
// Heuristic params for HistogramCombine().
const int num_tries_no_success = 8 + (quality >> 1);
const int iter_mult = (quality < 27) ? 1 : 1 + ((quality - 27) >> 4);
int num_pairs = (quality >> 1);
const int num_pairs = (quality < 25) ? 10 : (5 * quality) >> 3;
VP8LHistogramSet* const image_out =
VP8LAllocateHistogramSet(histo_image_raw_size, cache_bits);
if (image_out == NULL) return 0;
if (num_pairs > (histo_image_raw_size >> 2)) {
num_pairs = histo_image_raw_size >> 2;
}
num_pairs += 10;
// Build histogram image.
HistogramBuildImage(xsize, histo_bits, refs, image_out);
// Collapse similar histograms.